A liquid crystal display (LCD) is a device which converts various types of electrical information generated from various types of devices into visual information and displays the visual information, using changes in liquid crystal transmittance according to applied voltages.
Because the LCD is not self-emissive, the LCD is provided with a backlight unit (BLU) serving as a light emitting device which provides light to rear of a liquid crystal panel that displays images.
The BLU may be classified as an edge type or a direct type depending on position of light emitting diodes (LED) collectively serving as a light source.
In the edge type BLU, light source LEDs are disposed at side surfaces of a light guide plate, and a liquid crystal panel is irradiated by the light guide plate with the light from the LEDs by total internal reflection and the like.
The direct type BLU uses a diffusion plate instead of the light guide plate, and LEDs are disposed behind the liquid crystal panel. Accordingly, the rear surface of the liquid crystal panel is irradiated with LED light.
Recently, research into the direct type BLU for lowering cost, reducing power consumption, and slimming is actively ongoing. As a task for the research, a reflection type lens capable of covering a wide area with fewer light sources is being developed.
However, when a thickness of a BLU is 10 mm or less, the center of a lens becomes bright, resulting in a problem of generating Mura.